U.S. patent application number 15/139624 was filed with the patent office on 2017-11-02 for rotor assembly for a direct drive motor.
This patent application is currently assigned to WHIRLPOOL CORPORATION. The applicant listed for this patent is WHIRLPOOL CORPORATION. Invention is credited to Orlando Starke.
Application Number | 20170317539 15/139624 |
Document ID | / |
Family ID | 58192216 |
Filed Date | 2017-11-02 |
United States Patent
Application |
20170317539 |
Kind Code |
A1 |
Starke; Orlando |
November 2, 2017 |
ROTOR ASSEMBLY FOR A DIRECT DRIVE MOTOR
Abstract
A rotor assembly is provided for a motor of a laundry appliance.
The rotor assembly includes a rotor frame having a hub region that
extends radially outward from a central hub, and a cylindrical rim
extending axially from the hub region. The rotor assembly further
includes a yoke disposed at an inner surface of the cylindrical
rim, and a plurality of magnets disposed at an inner surface of the
yoke, wherein the yoke comprises a helically wound metal strip.
Inventors: |
Starke; Orlando; (Saint
Joseph, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WHIRLPOOL CORPORATION |
BENTON HARBOR |
MI |
US |
|
|
Assignee: |
WHIRLPOOL CORPORATION
BENTON HARBOR
MI
|
Family ID: |
58192216 |
Appl. No.: |
15/139624 |
Filed: |
April 27, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D06F 37/30 20130101;
H02K 1/278 20130101; H02K 15/03 20130101; H02K 21/12 20130101; H02P
27/06 20130101; H02K 1/27 20130101; H02K 15/08 20130101 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 15/08 20060101 H02K015/08; D06F 37/30 20060101
D06F037/30; H02K 15/03 20060101 H02K015/03; H02P 27/06 20060101
H02P027/06; H02K 21/12 20060101 H02K021/12 |
Claims
1. A motor for a laundry appliance, comprising: a stator assembly;
and a rotor assembly that rotates around the stator assembly, the
rotor assembly comprising: a central hub for securing the rotor
assembly to a drive shaft of the motor such that the rotor assembly
rotates about an axis of the drive shaft; a rotor frame comprising:
a hub region for receiving the central hub, the hub region
extending radially outward from the central hub, and a cylindrical
rim extending axially from the hub region so as to be coaxial with
the drive shaft; a yoke disposed at an inner surface of the
cylindrical rim; and a plurality of magnets disposed at an inner
surface of the yoke, wherein the yoke comprises a helically wound
metal strip.
2. The motor of claim 1, wherein the metal strip has a thickness in
the radial direction and has a width in the axial direction, and
the width in the axial direction is less than the thickness in the
radial direction.
3. The motor of claim 2, wherein the thickness of the metal strip
is between about 3 mm and about 7 mm.
4. The motor of claim 3, wherein the width of the metal strip is
between about 0.5 mm and about 2 mm.
5. The motor of claim 2, wherein the width of the metal strip is
between about 0.5 mm and about 2 mm.
6. The motor of claim 1, wherein the rotor frame is
injection-molded to form the rim around an outer surface of the
yoke.
7. The motor of claim 1, wherein the helically wound metal strip is
formed such that any air gaps between adjacent windings of the
metal strip are between about 2 .mu.m and about 10 .mu.m.
8. A laundry appliance comprising: a drum for receiving laundry;
and the motor of claim 1 for rotating the drum.
9. A rotor assembly for a motor of a laundry appliance, the motor
having a stator assembly having an outer surface about which the
rotor assembly rotates, the rotor assembly comprising: a central
hub for securing the rotor assembly to a drive shaft of the motor
such that the rotor assembly rotates about an axis of the drive
shaft; a rotor frame comprising: a hub region for receiving the
central hub, the hub region extending radially outward from the
central hub and having a circular outer periphery, and a
cylindrical rim extending axially from the outer periphery of the
hub region so as to be coaxial with the drive shaft, the
cylindrical rim having an inner surface facing towards the outer
surface of the stator assembly; a yoke disposed at the inner
surface of the cylindrical rim, the yoke having an inner surface
facing towards the outer surface of the stator assembly; and a
plurality of magnets disposed at the inner surface of the
cylindrical yoke, wherein the yoke comprises a helically wound
metal strip.
10. The rotor assembly of claim 9, wherein the metal strip has a
thickness in the radial direction and has a width in the axial
direction that is less than the thickness in the radial
direction.
11. The rotor assembly of claim 10, wherein the thickness of the
metal strip is between about 3 mm and about 7 mm.
12. The rotor assembly of claim 11, wherein the width of the metal
strip is between about 0.5 mm and about 2 mm.
13. The rotor assembly of claim 10, wherein the width of the metal
strip is between about 0.5 mm and about 2 mm.
14. The rotor assembly of claim 9, wherein the rotor frame is
injection-molded to form the rim around an outer surface of the
yoke.
15. The rotor assembly of claim 9, wherein the helically wound
metal strip is formed such that any air gaps between adjacent
windings of the metal strip are between about 2 .mu.m and about 10
.mu.m.
16. A laundry appliance comprising: a drum for receiving laundry;
and a motor for rotating the drum, wherein the motor comprises a
stator assembly and the rotor assembly of claim 9.
17. A method of making a rotor assembly comprising: forming a yoke
using a helically wound metal strip, the yoke having an outer
surface and an inner surface; disposing magnets about an outer
surface of an insert mold; positioning the yoke around the magnets
such that the inner surface of the yoke faces the magnets; placing
the insert mold with the magnets and the yoke into an injection
mold cavity; and injection molding a rotor frame where the rotor
frame has a cylindrical rim that extends along the outer surface of
the yoke.
18. The method of claim 17, wherein the step of forming the yoke
includes helically winding the metal strip around a mandrel and
removing the yoke from the mandrel.
19. The method of claim 18, wherein, in the step of forming the
yoke, the metal strip is guided onto the mandrel such that any air
gaps between adjacent windings of the metal strip are between about
2 .mu.m and about 10 .mu.m.
20. The method of claim 17, wherein the metal strip has a thickness
in the radial direction and has a width in the axial direction that
is less than the thickness in the radial direction.
Description
BACKGROUND
[0001] The present device generally relates to a rotor assembly for
a motor, and more specifically, to a rotor assembly for a direct
drive motor of a laundry appliance as well as a laundry appliance
incorporating the motor with the rotor assembly and a method of
making the rotor assembly.
SUMMARY
[0002] In at least one aspect, a motor for a laundry appliance is
provided, comprising a stator assembly, and a rotor assembly that
rotates around the stator assembly. The rotor assembly comprises a
central hub for securing the rotor assembly to a drive shaft of the
motor such that the rotor assembly rotates about an axis of the
drive shaft, and a rotor frame. The rotor frame comprises a hub
region for receiving the central hub, the hub region extending
radially outward from the central hub, and a cylindrical rim
extending axially from the hub region. The rotor assembly further
comprises a yoke disposed at an inner surface of the cylindrical
rim, and a plurality of magnets disposed at an inner surface of the
yoke, wherein the yoke comprises a helically wound metal strip.
[0003] In at least another aspect, a rotor assembly is provided for
a motor of a laundry appliance, where the motor has a stator
assembly having an outer surface about which the rotor assembly
rotates. The rotor assembly comprises a central hub for securing
the rotor assembly to a drive shaft of the motor such that the
rotor assembly rotates about an axis of the drive shaft, and a
rotor frame. The rotor frame comprises a hub region for receiving
the central hub, the hub region extending radially outward from the
central hub and having a circular outer periphery, and a
cylindrical rim extending axially from the outer periphery of the
hub region so as to be coaxial with the drive shaft, the
cylindrical rim having an inner surface facing towards the outer
surface of the stator assembly. The rotor assembly further
comprises a yoke disposed at the inner surface of the cylindrical
rim, the yoke having an inner surface facing towards the outer
surface of the stator assembly, and a plurality of magnets disposed
at the inner surface of the yoke, wherein the yoke comprises a
helically wound metal strip.
[0004] In at least another aspect, a method of making a rotor
assembly comprises forming a yoke using a helically wound metal
strip, the yoke having an outer surface and an inner surface;
disposing magnets about an outer surface of an insert mold;
positioning the yoke around the magnets such that the inner surface
of the yoke faces the magnets; placing the insert mold with the
magnets and the yoke into an injection mold cavity; and injection
molding a rotor frame where the rotor frame has a cylindrical rim
that extends along the outer surface of the yoke.
[0005] These and other features, advantages, and objects of the
present device will be further understood and appreciated by those
skilled in the art upon studying the following specification,
claims, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] In the drawings:
[0007] FIG. 1 is a top perspective view of a laundry appliance
according to one embodiment;
[0008] FIG. 2 is a cross-sectional view of an example of a direct
drive motor that may be used in the laundry appliance of FIG.
1;
[0009] FIG. 3 is a perspective view of a rotor assembly used in the
motor shown in FIG. 2;
[0010] FIG. 4 is a cross-sectional view of the rotor assembly shown
in FIG. 3 taken along line IV-IV;
[0011] FIG. 5 is an enlarged cross-sectional view of a region of
the rotor assembly shown in
[0012] FIG. 4 designated as area V;
[0013] FIG. 6 is an exploded perspective view of the rotor assembly
shown in FIGS. 3-5;
[0014] FIG. 7 is a schematic view of an apparatus for producing a
metal strip used in the rotor assembly shown in FIGS. 3-6;
[0015] FIG. 8A is a cross-sectional view of the apparatus shown in
FIG. 7 taken along line VIIIA;
[0016] FIG. 8B is a cross-sectional view of the apparatus shown in
FIG. 7 taken along line VIIIB;
[0017] FIG. 8C is a cross-sectional view of the apparatus shown in
FIG. 7 taken along line VIIIC;
[0018] FIG. 8D is a cross-sectional view of the apparatus shown in
FIG. 7 taken along line VIIID;
[0019] FIG. 8E is a cross-sectional view of the apparatus shown in
FIG. 7 taken along line VIIIE;
[0020] FIG. 9 is a perspective view of an apparatus for forming the
yoke used in the rotor assembly shown in FIGS. 3-5 using the metal
strip as formed using the apparatus shown in FIGS. 7-8E; and
[0021] FIG. 10 is an enlarged perspective view of the metal strip
corresponding to the area X in FIG. 9.
DETAILED DESCRIPTION OF EMBODIMENTS
[0022] For purposes of description herein the terms "upper,"
"lower," "right," "left," "rear," "front," "vertical,"
"horizontal," and derivatives thereof shall relate to the device as
oriented in
[0023] FIG. 1. However, it is to be understood that the device may
assume various alternative orientations and step sequences, except
where expressly specified to the contrary. It is also to be
understood that the specific devices and processes illustrated in
the attached drawings and described in the following specification
are simply exemplary embodiments of the inventive concepts defined
in the appended claims. Hence, specific dimensions and other
physical characteristics relating to the embodiments disclosed
herein are not to be considered as limiting, unless the claims
expressly state otherwise.
[0024] As indicated above, the embodiments described herein relate
to a rotor assembly for use in a direct drive motor of a laundry
appliance. FIG. 1 shows a laundry appliance 10 that happens to be
in the form of a washing appliance. In some embodiments, the
laundry appliance 10 may include additional and/or different
components than those shown in FIG. 1 and described herein. The
laundry appliance includes a drum 18 in which laundry is received.
The drum 18 is disposed in a tub 76 and is rotated by means of a
motor 16 as described further below.
[0025] In the illustrative embodiment shown in FIG. 1, the laundry
appliance 10 is a front-loaded appliance in which the drum 18 is
accessed through an opening defined in the front of the laundry
appliance 10. It should be appreciated that in other embodiments
the laundry appliance 10 may have other configurations. For
example, the laundry appliance 10 may be a top-loaded appliance in
which the drum 18 is accessed through an opening defined in the top
of the laundry appliance 10. Further, in the illustrative
embodiment, the rotational axis 62 (FIG. 2) of the drum 18 is
horizontal. It should be appreciated that the rotational axis may
have other configurations; for example, the rotational axis may be
vertical. The laundry appliance 10 may further include a user
interface panel 30 for a user to control the wash/dry cycles of the
appliance.
[0026] The motor 16 may be a direct drive permanent magnet
synchronous motor (also known as a brushless, alternating current
(AC) motor). As shown in FIG. 2, according to the various
embodiments, a motor 16 for the laundry appliance 10, such as a
direct drive, may include a drive shaft 60 that is coupled to a
drum 18 at a first end 64 of drive shaft 60. A rotor assembly 74
having a rotor frame 66 is coupled proximate a second end 68 of the
drive shaft 60. A central hub 72 is included within the rotor frame
66.
[0027] The drum 18 includes a cavity that is sized to receive
clothes and other laundry 20 to be washed or dried in the laundry
appliance 10. The drum 18 is set within a tub 76 that receives wash
water for cleaning the laundry set within the drum 18. The direct
drive motor 16 is attached proximate the tub 76, where a stator
assembly 78 of the direct drive motor 16 is coupled to a portion of
the tub 76, thereby substantially fixing the location of the stator
assembly 78. Disposed in the tub 76 is a bearing housing 80
including at least one bearing 82 that allows the drive shaft 60 to
be rotated within the wall 84 of the tub 76. As described further
below, the rotor assembly 74 includes magnets 86 that are in
magnetic communication with stator coils 88 of the stator assembly
78 and form a permanent synchronous motor 16. Each stator field
coil 88 of the motor 16 is separately electrically connected to an
inverter (not shown). During operation, the inverter supplies AC
power of the same frequency but with different phases to each
stator field coil 88 of the motor 16. The multi-phased AC power
flows through the stator field coils 88 of the motor 16 to produce
a rotating magnetic field; that is, the direction of the combined
magnetic field produced by the plurality of stator field coils 88
rotates. This rotating magnetic field interacts with the one or
more permanent magnets 86 and causes the rotor assembly 74 to
rotate. In this manner, as the rotor 74 rotates about the stator
assembly 78, the connection of the rotor assembly 74 to the drum 18
via the drive shaft 60 allows for the transfer of torque from the
rotor assembly 74 to the drive shaft 60 and, in turn, to the drum
18 such that the drum 18, drive shaft 60, and rotor assembly 74
rotate about rotation axis 62. The rotation axis 62 corresponds to
"the axial direction" as used herein. Moreover, the term "the
radial direction" refers to directions that are perpendicular to
rotation axis 62.
[0028] It is contemplated that other types of electric motors 16
can be utilized where the motor 16 includes a rotor assembly 74
that rotates relative to a stator assembly 78. Such motors 16 can
include, but are not limited to, direct drive motors, motors that
are coupled to transmissions, belt-drive motors, and other similar
electric motors. Additionally, the various aspects of the
embodiments can be used in various orientations of motor 16,
including motors that are positioned along a vertical axis, a
horizontal axis and/or an angled axis.
[0029] As shown in FIGS. 3-6 and described above, the rotor
assembly 74 includes the central hub 72 for securing the rotor
assembly to the drive shaft 60 of the motor 16 such that the rotor
assembly 74 rotates about the axis 62 of the drive shaft 60. As
also described above, the rotor assembly 74 further includes a
rotor frame 66 and a plurality of magnets 86. The rotor frame 66
includes a hub region 92 for receiving the central hub 72. The hub
region 92 extends radially outward from the central hub 72 and has
a circular outer periphery. A portion 94 of hub region 92 may have
a thinner profile than the portion surrounding central hub 72. The
rotor frame 66 further includes a cylindrical rim 96 extending
axially from the outer periphery of the hub region 92 so as to be
coaxial with the rotational axis 62 of the drive shaft 60. The
cylindrical rim 96 has an inner surface facing towards the
cylindrical outer surface of the stator assembly 78.
[0030] The rotor assembly further includes a cylindrical yoke 100
(also known as a back iron) disposed adjacent the inner surface of
the cylindrical rim 96. The cylindrical yoke 100 has an inner
surface facing towards the cylindrical outer surface of the stator
assembly 78. The plurality of magnets 86 are disposed adjacent the
inner surface of the cylindrical yoke 100. As described further
below, the cylindrical yoke 100 includes a metal strip 102
configured in the form of a helix.
[0031] As shown in FIGS. 5 and 10, the metal strip 102 has a
thickness T in the radial direction and a width W in the axial
direction. The width of metal strip 102 may be less than the
thickness. For example, the thickness of the metal strip 102 may be
between about 3 mm and about 7 mm, and the width may be between
about 0.5 mm and about 2 mm. The metal strip 102 as configured in
the form of a helix may be formed such that any air gaps between
adjacent windings of the metal strip 102 are between about 2 .mu.m
and about 10 .mu.m. This may be accomplished by winding the metal
strip around a cylindrical mandrel 110 as shown in FIG. 9, while
using member 112 to guide the metal strip 102 onto the mandrel 110
so as to obtain the appropriate spacing relative to the last
winding applied to the mandrel 110. Note that member 112 may be
forked such the metal strip 102 is guided between to prongs of the
forked end of member 112. The mandrel 110 may have a radially
protruding flange 114 at one or both ends in order to press the
first winding of the metal strip 102 against the flange 114.
[0032] Helical yoke 100 may have an axial height H (FIG. 6) of
about 20 mm to about 70 mm and a radial thickness of about 0.5 mm
to about 2 mm. The radial thickness corresponds to the thickness of
the metal strip 102. If the metal strip has a thickness of 0.5 mm
and a yoke with an axial height of 30 mm was desired, for example,
the metal strip 102 would include approximately 60 windings with no
air gaps between the windings. The height and thickness of yoke 100
are flexible to accommodate the magnetic flux density as requested
by the application. To help assure the stiffness and alignment
while the layers are stacked, some fixation features may be added.
For example, rivet pins may be added on the yoke to provide welding
lines on the outer face of the yoke. Another option would be to
apply some adhesive bond. In general, however, the bonding among
the back iron, magnets and the rotor frame 66 is done by a
polymeric over-molding process to contribute to the desired
stiffness of the rotor assembly 74.
[0033] One example of a method for making rotor assembly 74
includes forming a helical yoke 100 using a metal strip 102, the
yoke 100 having an outer surface and an inner surface; disposing
magnets 86 about an outer surface of an insert mold; positioning
the helical yoke 100 around the magnets 86 such that the inner
surface of the helical yoke 100 faces the magnets 86; placing the
insert mold with the magnets 86 and the helical yoke 100 into an
injection mold cavity; and injection molding a plastic rotor frame
66 where the rotor frame 66 has a cylindrical rim 96 that extends
along the outer surface of the helical yoke 100.
[0034] As mentioned above, the yoke 100 may be pre-formed by
winding the metal strip 102 around a mandrel and then slid axially
over the outer surfaces of the magnets 86. In a variation of the
above method, the yoke may be formed by winding the metal strip
around the magnets 86 themselves instead of a mandrel. As yet
another variation, the rotor frame 66 may be pre-formed and the
yoke 100 and magnets 86 may be press-fit into the rim 96 of frame
66.
[0035] The magnets 86 may be made of any conventional magnetic
material and may be provided in various forms including in a magnet
chain as described in U.S. Patent Application Publication No. US
2015/0089794 A1, the entire disclosure of which is incorporated
herein by reference.
[0036] The metal strip 102 may be made of any ferromagnetic steel
or other metal known to be suitable for use as a yoke. A method of
forming the metal strip 102 is described below with reference to
FIGS. 7 and 8A-8E.
[0037] The metal strip 102 may be made by various methods. One
method is to simply cut a plurality of metal strips from a large
sheet of metal using an industrial slitting apparatus. Such an
apparatus can provide metal strips of and dimension down to about 9
mm when cutting a sheet of about 0.5 mm to 2 mm thickness. However,
in order to obtain metal strips with a dimension of less than 9 mm,
the method shown in to FIGS. 7 and 8A-8E may be used.
[0038] As shown in FIG. 7, a steel rod having a substantially
circular cross-section (as shown in FIG. 8A) is fed through a first
set of pressing rollers 120a and 120b, which presses the steel rod
to begin to flatten it as shown in FIG. 8B. Then the steel is fed
through successive second, third, and fourth sets of pressing
rollers 120c-120h where the steel is further flattened to a thinner
profile as shown in FIGS. 8C-8E, until the desired dimensions of
the metal strip 102 are obtained. It will be appreciated that fewer
or greater sets of rollers may be used to obtain the desired
cross-sectional shape. As noted above, the metal strip may have a
thickness (the horizontal dimension in FIG. 8E) of about 3 mm to
about 7 mm and a width (the vertical dimension in FIG. 8E) of about
0.5 mm to about 2 mm. The cross-sectional area of the starting
steel rod will correspond to the desired cross-sectional area of
the metal strip.
[0039] An annealing step may be performed on the metal strip 102 to
provide the steel the desired properties. Once the metal strip 102
is formed, the helical yoke 100 is created by bending this strip
102 with its rectangular cross section on direction of its width
(not in the thickness direction) on a mandrel or the like as
discussed above. The strip will thus be bent and wound into the
desired diameter of the yoke. Some welding may be performed around
the external surface of the final helical yoke 100. One may then
conform the external diameter by fitting the helical yoke 100
inside a template.
[0040] The above-described rotor assembly 74 satisfies several
design goals. First, it allows for consistent spacing between the
outer diameter of the stator assembly 78 and the inner diameter of
the rotor assembly 74. This is accomplished by ensuring circularity
of the rotor assembly 74 and the stator assembly 78, ensuring the
rotor assembly 74 has sufficient radial mechanical stiffness and
rigidity to avoid distortion of its circularity while rotating, and
reducing vibration of the rotor assembly 74. Compared to yokes made
of joined arc segments, the helical yoke 100 has better
circularity. Second, the rotor assembly 74 reduces noise by having
improved radial stiffness and by reducing vibration. Third, by
providing consistent spacing between the outer diameter of the
stator assembly 78 and the inner diameter of the rotor assembly 74,
the electromagnetic performance is improved and hence the
efficiency of the motor 16 is improved. Also, the cost of producing
the motor may be lowered and temperature management may be
improved. The cost is lowered by using less material as compared to
yokes made of joined arc segments and by having lower run out
variation.
[0041] It will be understood by one having ordinary skill in the
art that construction of the described device and other components
is not limited to any specific material. Other exemplary
embodiments of the device disclosed herein may be formed from a
wide variety of materials, unless described otherwise herein.
[0042] For purposes of this disclosure, the term "coupled" (in all
of its forms, couple, coupling, coupled, etc.) generally means the
joining of two components (electrical or mechanical) directly or
indirectly to one another. Such joining may be stationary in nature
or movable in nature. Such joining may be achieved with the two
components (electrical or mechanical) and any additional
intermediate members being integrally formed as a single unitary
body with one another or with the two components. Such joining may
be permanent in nature or may be removable or releasable in nature
unless otherwise stated.
[0043] It is also important to note that the construction and
arrangement of the elements of the device as shown in the exemplary
embodiments is illustrative only. Although only a few embodiments
of the present innovations have been described in detail in this
disclosure, those skilled in the art who review this disclosure
will readily appreciate that many modifications are possible (e.g.,
variations in sizes, dimensions, structures, shapes and proportions
of the various elements, values of parameters, mounting
arrangements, use of materials, colors, orientations, etc.) without
materially departing from the teachings and advantages of the
subject matter recited. For example, elements shown as integrally
formed may be constructed of multiple parts or elements shown as
multiple parts may be integrally formed, the operation of the
interfaces may be reversed or otherwise varied, the length or width
of the structures and/or members or connector or other elements of
the system may be varied, the nature or number of adjustment
positions provided between the elements may be varied. It should be
noted that the elements and/or assemblies of the system may be
constructed from any of a wide variety of materials that provide
sufficient strength or durability in any of a wide variety of
colors, textures, and combinations. Accordingly, all such
modifications are intended to be included within the scope of the
present innovations. Other substitutions, modifications, changes,
and omissions may be made in the design, operating conditions, and
arrangement of the desired and other exemplary embodiments without
departing from the spirit of the present innovations.
[0044] It will be understood that any described processes or steps
within described processes may be combined with other disclosed
processes or steps to form structures within the scope of the
present device. The exemplary structures and processes disclosed
herein are for illustrative purposes and are not to be construed as
limiting.
[0045] It is also to be understood that variations and
modifications can be made on the aforementioned structures and
methods without departing from the concepts of the present device,
and further it is to be understood that such concepts are intended
to be covered by the following claims unless these claims by their
language expressly state otherwise.
[0046] The above description is considered that of the illustrated
embodiments only. Modifications of the device will occur to those
skilled in the art and to those who make or use the device.
Therefore, it is understood that the embodiments shown in the
drawings and described above is merely for illustrative purposes
and not intended to limit the scope of the device, which is defined
by the following claims as interpreted according to the principles
of patent law, including the Doctrine of Equivalents.
* * * * *